You can see his famous drawings, which appear in the New York Times, here: http://www.behaviorgap.com/shop/
Importantly, his company is called the Behavior Gap. This is the concept of a private investor’s behaviour when managing their own investments, resulting in them earning LOWER rates of return than the markets, or more specifically the funds they are investing in.
I quoted some research in a recent blog on DIY Investing where the average investor hugely underperformed the fund they were invested in. This doesn’t surprise me, because it is so easy to do what feels right. We are programmed to react emotionally in our decision making process. We want to buy a fund when it has done well and sell a fund when it performs poorly. That is a very common path for investors to take and a path that leads to what Carl refers to as the behaviour gap.